1. Field of Invention
The present invention relates to an etching-stop technique, and particularly to a liquid-based gravity-driven etching-stop technique for controlling a microstructure dimension of a device.
2. Related Art
With the increasing development of science and technology, the research tends towards the miniaturization, and the research and development of the Micro-ElectroMechanical System (MEMS) have been increased significantly. The microstructures produced by the MEMS technique include a micro sensor, a micro actuator, an atomic force probe, and the like, which can be used in various fields such as biological medicine, aerospace, electronics, and environmental engineering.
For the current technique for controlling the etching degree of a microstructure, such as the thickness of a cantilever beam or suspend membrane structure, the etching degree is conventionally measured by manually observing the images of the etched parts using a microscope or a scanning electronic microscope (SEM), and determining whether the etching degree is in accordance with the standard. Alternatively, the etching rate of the material used and its proper etchant is measured as the reference of the time required to carry out the etching. However, most of the above methods are using empirical value obtained as reference of the process, and it is difficult to control the etching thickness efficiently when etching the structure.
In order to actively control the thickness of a suspend membrane or cantilever beam structure, in the current micro-electromechanical process, the ion implantation combined with electrochemical etching or a Silicon on isolation (SOI) is used for controlling, thus resulting in high manufacturing cost and technical difficulties.
Therefore, a method is developed to control the etching degree, in which etching trenches are made in a wafer. The etching trenches are portrayed previously around the device of the wafer to be etched, and then etched until they are etched through to drop the device, which is then taken out and washed. However, in this method, it is necessary to visually observe whether the device has fallen, and the device has to be taken out immediately. The etching is still continued during the time interval between taking-out and washing, therefore influencing the precision of the device.